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Dave Brunswick attempts to unclog the centrifuge sludge feed at Wilsonville's wastewater treatment plant Tuesday morning. Bids to upgrade and expand the facility are due at the end of the month.

WILSONVILLE -- It's tough to find a breath of fresh air in Old Town. Its next-door neighbor smells.

Bids to replace or repair much of the ailing plant are due in two weeks, the first step in a proposed $63 million upgrade. Meanwhile, the city has spent more than $300,000 repairing the plant's most recent onslaught of malfunctions.

"The plant is falling apart," said Delora Kerber, the city's public works director. "We're at critical mass."

When the plant first started treating sewage in 1971, there were 1,000 people flushing toilets in Wilsonville. Today, more than 18,000 residents and thousands more employees are flushing out the wastewater plant piece by piece.

Yet as the upgrade project enters its earliest stages, some Wilsonville residents question how the city plans to finance it. A five-year forecast published by the city shows sewer rates could double within the next few years.

The city plans to sell bonds for the project. To help cover costs, the city's five-year forecast outlines doubling sewer rates by 2014, implementing 25 percent increases during each of the next three years. A Wilsonville household that paid $41 a month in sewer fees last year would pay $88 under the plan, the forecast says.

The move would also inject $5 million into the sewer's annual operating fund, bringing it to nearly $10.5 million by 2014.

Steve Van Wechel, president of the Old Town Neighborhood Association, said he considers the rate increases a "necessary evil." A deliveryman recently asked Van Wechel whether the local smell came from dead animals.

"If you're going to get rid of the smell, you're going to have to do some major plant upgrades," Van Wechel said.

In the meantime, equipment continues to malfunction throughout the 10-acre wastewater treatment site bounded by Interstate 5, the Willamette River and a rocky landscape. In the four decades since the plant was built, the city has added some equipment and updated some of the plant's processes.

During a recent plant tour, three men worked to repair a machine that had shorted itself five days earlier. Another man attempted to unclog the sludge feed, which carries the treated solids from one end of the plant into trucks on the opposite end.

Often, workers must retrofit parts to repair the broken equipment, diverting time from normal upkeep, said Michael Bowers, the community's development director. "We're kind of custom-fitting things into 1970s concrete structures," Bowers said.

Many of those structures have no backups, Kerber said. The plant enters scramble mode when things go wrong, she said. And that can be costly. Recent repair costs include:

$4,000 every day for nearly four weeks to truck liquid biosolids out of the plant after the centrifuge failed in December. The machine, which spins the water out of biosolids, began functioning again earlier this month.

$40,000 to mend the centrifuge last summer.

$200,000 to replace a failed sand filter with a rental machine and to fix a second filter. The sand filters clarify the treated water before it's discharged into the Willamette in the summer.

Still, Steve Hurst, one of the city's four councilors, said the constant repairs could keep the plant functioning for several years -- without a multimillion-dollar renovation.

"There have been more issues as of late, but whether that is completely accurate, or whether that is a justification to pump more money into it, I don't know," Hurst said, acknowledging that the plant eventually would need a major update to sustain the city's growth.

But he questioned a decision from the project's outset to choose one firm to design, build and operate the plant. Two companies, CH2M Hill and Veolia Water, are expected to submit their bids by the end of the month.

"If either of those bids are more than we can afford, we don't have a well-researched design-build option to jump into immediately," Hurst said.

Van Wechel also questioned the one-firm option because he felt it would take a certain amount of control from the city.

Yet Bowers and Kerber agreed the benefits of using a single firm outweigh any negative effects. The method links construction with operation to create a smooth process, Kerber said. Ownership of the plant will remain with the city.

The city's water treatment plant, built in 2002, used the design-build-operate method. "We're essentially applying the same lessons we learned," Bowers said.

The city council will begin reviewing the proposals this spring. Van Wechel expected little opposition from Old Town residents. "We don't like the smell," he said.

Hurst called it "borderline unbearable."

"I'm just waiting with bated breath to see what these bids look like," he said.